In the formation of three-dimensional integrated circuits (3DICs), the device dies that have integrated circuits formed therein are packaged with other package components such as interposers, package substrates, device dies, printed circuit boards (PCBs), and the like. In some of the packages, the package components also need to be bonded to each other. For example, a device die may be bonded to an interposer, which is further bonded to a package substrate. The package substrate with the interposer and the device die bonded thereon may further be bonded to a PCB.
The bonding between the package components may be performed through flip-chip bonding, which may be metal-to-metal bonding or solder bonding. Reliable bonding methods are currently explored.